My brother's X5 has a defective AC. Sometimes when you turn on the car, the AC fails to switch on even when you have it on max. The weird thing is that the rear vents works fine but the main front vents fail to deliver any air. However this fluctuates as the AC sometimes works when you drive the car for some time. The air is cool and everything is perfect. I think it's a computer problem. Any idea as to why this happens and how to get it fixed?

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